1. Field of the Invention
The present invention relates to a buffer circuit, a driver circuit, and a semiconductor testing apparatus. The present invention specifically relates to a buffer circuit and a driver circuit that can deal with input and output signals with a large voltage swing, and a semiconductor testing apparatus including such a driver.
2. Related Art
FIG. 1 shows the configuration of a conventional buffer circuit 100. The buffer circuit 100 includes an input terminal 101, a transistor 102, a schottky diode 104, a constant current source 106, a constant current source 108, a schottky diode 110, a transistor 112, a transistor 114, a schottky diode 116, a schottky diode 118, a transistor 120, and an output terminal 122.
The transistor 102 is an NPN transistor. The base electrode of the transistor 102 is connected to the input terminal 101, the collector electrode is connected to a positive power supply voltage (Vcc), and the emitter electrode is connected to the anode of the schottky diode 104. The schottky diode 104 is connected at the anode to the emitter electrode of the transistor 102, and connected at the cathode to the base electrode of the transistor 120 and the constant current source 106. The constant current source 106 is connected to the cathode of the schottky diode 104 and a negative power supply voltage (Vee) so as to be positioned therebetween. The constant current source 106 causes a constant current to flow, between the positive power supply voltage and the negative power supply voltage, into the transistor 102 and the schottky diode 104.
The transistor 112 is a PNP transistor. The base electrode of the transistor 112 is connected to the input terminal 101, the collector electrode is connected to the negative power supply voltage, and the emitter electrode is connected to the cathode of the schottky diode 110. The schottky diode 110 is connected at the anode to the constant current source 108, and connected at the cathode to the emitter electrode of the transistor 112. The constant current source 108 is connected to the positive power supply voltage and the anode of the schottky diode 110 so as to be positioned therebetween. The constant current source 108 causes a constant current to flow, between the positive power supply voltage and the negative power supply voltage, into the schottky diode 110 and the transistor 112.
The transistor 114 is an NPN transistor. The base electrode of the transistor 114 is connected to the constant current source 108 and the anode of the schottky diode 110, the collector electrode is connected to the positive power supply voltage, and the emitter electrode is connected to the schottky diode 116. The schottky diode 116 is connected at the anode to the emitter electrode of the transistor 114, and connected at the cathode to the output terminal 122. The schottky diode 118 is connected at the anode to the output terminal 122, and connected at the cathode to the emitter electrode of the transistor 120. The transistor 120 is a PNP transistor. The base electrode of the transistor 120 is connected to the constant current source 106 and the cathode of the schottky diode 104, the emitter electrode is connected to the cathode of the schottky diode 118, and the collector electrode is connected to the negative power supply voltage. Here, the currents supplied from the constant current sources 106 and 108 are substantially the same. According to this construction, the transistor 114, the schottky diode 116, the schottky diode 118, and the transistor 120 are supplied with a constant current all the time.
Here, it is assumed that in the above-described buffer circuit 100, the positive power supply voltage is +19 V, the negative power supply voltage is −6.5 V, and the input signal (input) and the output signal (output) have a voltage in a range from −3 V to +15 V. When a voltage decrease due to the transistors is 0.8 V, and a voltage decrease due to the schottky diodes is 0.5 V, the base voltage of the transistor 114 ranges from −1.7 V to +16.3 V, and the base voltage of the transistor 120 ranges from −4.3 V to +13.7 V.
FIG. 2 shows the configuration of a conventional buffer circuit 200. The buffer circuit 200 includes an input terminal 201, a transistor 202, a schottky diode 204, a resistance 206, a schottky diode 208, a constant current source 210, a constant current source 212, a schottky diode 214, a resistance 216, a schottky diode 218, a transistor 220, a transistor 222, a transistor 224, a schottky diode 226, a schottky diode 228, a transistor 230, a transistor 232, and an output terminal 234.
The transistor 202 is an NPN transistor. The base electrode of the transistor 202 is connected to the input terminal 201, the collector electrode is connected to a positive power supply voltage (Vcc), and the emitter electrode is connected to the anode of the schottky diode 204. The schottky diode 204 is connected at the anode to the emitter electrode of the transistor 202, and connected at the cathode to the base electrode of the transistor 230 and the resistance 206. The resistance 206 is connected to the cathode of the schottky diode 204 and the anode of the schottky diode 208 so as to be positioned therebetween. The schottky diode 208 is connected at the anode to the resistance 206, and connected at the cathode to the base electrode of the transistor 232 and the constant current source 210. The constant current source 210 is connected to the cathode of the schottky diode 208 and a negative power supply voltage (Vee) so as to be positioned therebetween. The constant current source 210 causes a constant current to flow, between the positive power supply voltage and the negative power supply voltage, into the transistor 202, the schottky diode 204, the resistance 206 and the schottky diode 208.
The transistor 220 is a PNP transistor. The base electrode of the transistor 220 is connected to the input terminal 201, the collector electrode is connected to the negative power supply voltage, and the emitter electrode is connected to the cathode of the schottky diode 218. The schottky diode 218 is connected at the cathode to the emitter electrode of the transistor 220, and connected at the anode to the base electrode of the transistor 224 and the resistance 216. The resistance 216 is connected to the cathode of the schottky diode 214 and the anode of the schottky diode 218 so as to be positioned therebetween. The schottky diode 214 is connected at the cathode to the resistance 216, and connected at the anode to the base electrode of the transistor 222 and the constant current source 212. The constant current source 212 is connected to the anode of the schottky diode 214 and the positive power supply voltage so as to be positioned therebetween. The constant current source 212 causes a constant current to flow, between the positive power supply voltage and the negative power supply voltage, into the schottky diode 214, the resistance 216, the schottky diode 218, and the transistor 220.
The transistor 222 is an NPN transistor. The base electrode of the transistor 222 is connected to the constant current source 212 and the anode of the schottky diode 214, the collector electrode is connected to the positive power supply voltage, and the emitter electrode is connected to the collector electrode of the transistor 224. The transistor 224 is an NPN transistor. The base electrode of the transistor 224 is connected to the resistance 216 and the anode of the schottky diode 218, the collector electrode is connected to the emitter electrode of the transistor 222, and the emitter electrode is connected to the anode of the schottky diode 226. The schottky diode 226 is connected at the anode to the emitter electrode of the transistor 224, and connected at the cathode to the output terminal 234 and the anode of the schottky diode 228. The schottky diode 228 is connected at the anode to the cathode of the schottky diode 226 and the output terminal 234, and connected at the cathode to the emitter electrode of the transistor 230. The transistor 230 is a PNP transistor. The base electrode of the transistor 230 is connected to the cathode of the schottky diode 204 and the resistance 206, the emitter electrode is connected to the cathode of the schottky diode 228, and the collector electrode is connected to the emitter electrode of the transistor 232. The transistor 232 is a PNP transistor. The base electrode of the transistor 232 is connected to the cathode of the schottky diode 208 and the constant current source 210, the emitter electrode is connected to the collector electrode of the transistor 230, and the collector electrode is connected to the negative power supply voltage. Here, the currents supplied from the constant current sources 210 and 212 are substantially the same. According to this construction, the transistor 222, the transistor 224, the schottky diode 226, the schottky diode 228, the transistor 230 and the transistor 232 are supplied with a constant current all the time.
Here, it is assumed that in the above-described buffer circuit 200, the positive power supply voltage is +19 V, the negative power supply voltage is −6.5 V, and the input signal (input) and the output signal (output) have a voltage in a range from −3 V to +15 V. When a voltage decrease due to the transistors is 0.8 V, and a voltage decrease due to the schottky diodes is 0.5 V, the base voltage of the transistor 224 ranges from −1.7 V to +16.3 V, the base voltage of the transistor 230 ranges from −4.3 V to +13.7 V, the base voltage of the transistor 222 ranges from −0.9 V to +17.1 V, and the base voltage of the transistor 232 ranges from −5.1 V to +12.9 V.
Since no prior art documents related to the present invention have been found, the explanation regarding such documents will be omitted.
Recent development of a higher-speed semiconductor device has created a demand for a higher-speed buffer circuit to be used in a driver circuit that is included in a semiconductor testing apparatus and supplies a test signal for testing the semiconductor device. Since such a buffer circuit has been increasingly formed by a chip, it is difficult to increase the permissible voltage level of the base voltages of the transistors used in the buffer circuit in addition to realization of higher-speed configuration.
In the buffer circuit 100 shown in FIG. 1, the voltage swing of the input signal is directly reflected in the base voltages of the transistors 114 and 120. This makes it impossible to increase the voltage swing of the input signal. Accordingly, the buffer circuit 100 can not output an output signal having a large voltage swing. The buffer circuit 200 shown in FIG. 2 additionally has a tracking circuit, and thus can maintain the base voltages of the transistors 224 and 230 at a constant level. However, the voltage swing of the input signal is directly reflected in the base voltages of the transistors 222 and 232. This makes it impossible to increase the voltage swing of the input signal. As a result, the buffer circuit 200 can not output an output signal having a large voltage swing.